In 1954,R. P. Kraft found astellar classification of F7 Ib at peak brightness,[18] matching thespectrum of an F-typesupergiant star. The class of the star varies over the course of a pulsation cycle, ranging down to G8 Ib at minimum brightness.[4] R. P. Kraft in 1956 identified a doubling of certain spectral lines, which he explained as the result of a falling shell of matter from a prior pulsation cycle that is colliding with thephotosphere.[19] Unlike most cepheid variables that undergo a singleshock per cycle, X Cyg has been found to undergo a double shock.[20]
No orbiting companion has been identified with a period of ten years or less.[21] The star showscirrus with tentative evidence for extended emission ofinfrared.[22]
^abKovtyukh, V. V.; et al. (January 2005), "Phase-dependent Variation of the Fundamental Parameters of Cepheids. II. Periods Longer than 10 Days",The Astronomical Journal,129 (1):433–453,Bibcode:2005AJ....129..433K,doi:10.1086/426339,S2CID120666782.
^abBreitfellner, M. G.; Gillet, D. (October 1993), "Atmospheric motions in classical cepheid stars. III. A very large amplitude star : X Cygni",Astronomy and Astrophysics,277: 553,Bibcode:1993A&A...277..553B.
Meyer, Ralf (December 2005), "X Cyg: observations from 1886 until today",Open European Journal on Variable Stars,13: 1,Bibcode:2005OEJV...13....1M.
Turner, David G. (July 1998), "A Search for Stars Physically Associated with the 16 Day Cepheid X Cygni. II. Clusters in the Field",The Astronomical Journal,116 (1):274–283,Bibcode:1998AJ....116..274T,doi:10.1086/300438,S2CID123331380.
Wallerstein, G.; et al. (August 1984), "A search for evidence of the neon-sodium cycle in the Cepheid X Cygni",Publications of the Astronomical Society of the Pacific,96:613–617,Bibcode:1984PASP...96..613W,doi:10.1086/131392,S2CID120641485.
Evans, N. R. (June 1984), "X Cygni: duplicity, period stability and atmospheric velocity structure",Astrophysical Journal,281:760–765,Bibcode:1984ApJ...281..760E,doi:10.1086/162154.
Turner, D. G. (May 1983), "A search for stars physically associated with the 16-day Cepheid X Cygni. I. Luminous Stars in the field",Astronomical Journal,88:650–654,Bibcode:1983AJ.....88..650T,doi:10.1086/113353.
Benz, W.; Mayor, M. (July 1982), "Turbulence variations for the three cepheids SV Vul, X CYG and del Cep",Astronomy and Astrophysics,111:224–228,Bibcode:1982A&A...111..224B.
Masani, A.; et al. (February 1968), "The Masses of BM Cas, X Cyg, RT Aur, RR Lyr",Information Bulletin on Variable Stars,258: 1,Bibcode:1968IBVS..258....1M.
Masani, A.; et al. (October 1966), "Determination of the Mass and the Model of the Variables: RT Aurigae, Eta Aquilae, X Cygni, Mira Ceti and BM Cassiopeiae of Pop.I, and RR Lyrae and Two Typical Variables of Pop. II",Information Bulletin on Variable Stars,162: 1,Bibcode:1966IBVS..162....1M.
